1) Field of the Invention
The present invention relates to a structural member with an integrated electrical circuit and, in particular, to a structurally integrated circuit including multiple electrical devices that are electrically connected by electrodes to one or more electrical buses.
2) Description of Related Art
Electrical devices are often used in conjunction with a structural member. For example, electrical devices such as sensors and actuators can be embedded within, mounted on, or otherwise structurally integrated with the structure of a vehicle such as an airplane, spacecraft, land vehicle, ship, and the like. Other examples of electrical devices mounted in conjunction with a structural member can include machinery, buildings, and the like. The sensors can be used to detect temperature, motion, stress, strain, damage, and the like at different locations throughout the structure. The actuators can be used to adjust various control portions of the structure such as an elevator, rudder, aileron, helicopter rotor, door, or valve. Data generated by the electrical devices is typically communicated via electrical wires from the devices to a computer or other circuit device for processing. Similarly, control signals and electrical power are typically transmitted via electrical wires from the computer, power supply, and/or other circuit device to the actuators and sensors. Thus, a network of wires is often required for controlling and monitoring the electrical devices. Each wire usually includes one or more conductive strands, for example, copper strands, which are covered with an insulative jacket. Parallel wires can be held in groups with bundle fasteners, such as cable tie straps or shrink tubing. Fasteners such as clips, ties, and the like are often used to connect the wires or bundles of wires to the structural member at successive locations along the length of the wires so that the position of the wires is maintained. In some cases, an extensive and complex network of wires may be required.
In some applications, however, it is difficult or impractical to connect the wires to the structural member. For example, the structural member may not define any interior cavities through which the wires can be passed, and the environmental conditions outside the structural member may be harsh, for example, excessively warm or cold or subject to mechanical stress, moisture, or corrosive agents. In addition, the weight and size of the wires may negatively affect the performance of the structural member. Further, in applications where the structural member undergoes significant or repeated mechanical stress, the resulting strains in the wires can break the wires regardless of whether the wires are connected to the structural member.
One illustrative example is a blade of a helicopter rotor, which is rotated quickly around a hub of the rotor. In some cases, it may be desirable to provide wires that extend along the length of the blade, for example, to monitor sensors or control actuators in or on the blade. The wires cannot be connected to the outside of the blade because of the external conditions, e.g., wind, moisture, and the like. Further, the blade undergoes significant stress due to centripetal and aerodynamic forces. If the wires are not connected successively or continuously along the length of the blade, each wire will be strained due to the inertial force that results from the rotation and vibration. On the other hand, if the wires are connected to the blade, the wires will be strained at the same rate as the blade. In either case, the stress that results in the wires can break or fatigue the wires, rendering the electrical devices ineffective.
Thus, there exists a need for a structurally integrated circuit that can be provided in a structural member for transmitting electrical signals or power. The circuit should be capable of functioning in harsh environmental conditions that include strain and temperature variations, moisture, and corrosive agents. The structurally integrated circuit should also be adaptable to structural members that do not include internal passages for wiring. The circuit should be capable of providing a complex electrical network in which multiple electrical devices are connected to one or more buses. Further, the circuit should resist failure, even when the structural member is subjected to significant or repeated stresses.